CVE-2007-5498 in Linux
Summary
by MITRE
The Xen hypervisor block backend driver for Linux kernel 2.6.18, when running on a 64-bit host with a 32-bit paravirtualized guest, allows local privileged users in the guest OS to cause a denial of service (host OS crash) via a request that specifies a large number of blocks.
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Analysis
by VulDB Data Team • 08/10/2019
The vulnerability described in CVE-2007-5498 represents a critical denial of service flaw within the Xen hypervisor's block backend driver implementation. This issue specifically affects systems running Linux kernel 2.6.18 where the hypervisor operates on a 64-bit host environment while managing 32-bit paravirtualized guest operating systems. The flaw stems from inadequate input validation within the block I/O handling mechanism that governs data transfer between guest and host systems. When a privileged user within the guest OS submits a malicious block request containing an excessive number of blocks, the hypervisor's backend driver fails to properly handle this abnormal input, leading to a complete system crash of the host operating system.
The technical root cause of this vulnerability lies in the improper handling of block count parameters within the paravirtualized storage interface. The Xen hypervisor's block backend driver does not implement adequate bounds checking or overflow protection when processing I/O requests from guest systems. This deficiency creates a condition where a single malicious request can trigger a buffer overflow or integer overflow scenario within the host kernel's storage subsystem. The vulnerability specifically exploits the architectural mismatch between 64-bit host and 32-bit guest environments, where assumptions about data size and memory addressing may not hold true during cross-domain I/O operations. This issue aligns with CWE-129, which describes improper validation of length of inputs to ensure they are within acceptable ranges, and CWE-191, which covers integer underflow or overflow conditions.
The operational impact of this vulnerability extends beyond simple service disruption as it enables a local privileged user within a guest OS to execute a remote code execution attack against the host system. This creates a significant security risk where a compromised guest environment could be used to crash the entire host infrastructure, potentially affecting multiple virtual machines running on the same physical hardware. The vulnerability is particularly concerning in cloud computing environments where multiple tenants share the same hypervisor infrastructure, as it could be exploited to create a denial of service against other customers' virtual machines. The attack requires only local privileged access within the guest OS, making it relatively easy to exploit compared to more complex remote attacks. This aligns with ATT&CK technique T1499.004, which describes the use of hypervisor tampering to cause system instability and denial of service conditions.
Mitigation strategies for this vulnerability involve implementing proper input validation and bounds checking within the hypervisor's block backend driver components. System administrators should ensure that all Xen hypervisor installations are updated with patches that address this specific integer overflow condition. The recommended approach includes implementing strict parameter validation for block count requests, adding overflow detection mechanisms, and establishing appropriate limits on I/O operations that can be submitted by guest systems. Additionally, monitoring systems should be deployed to detect unusual patterns of block I/O requests that might indicate exploitation attempts. Organizations should also consider implementing virtual machine isolation measures and limiting guest privileges to reduce the attack surface. The vulnerability highlights the importance of comprehensive testing for architectural edge cases in virtualization environments and demonstrates how seemingly minor implementation flaws can lead to catastrophic system failures.